Method and device for controlling a volume flow of a wetting fluid during adiabatic cooling

ABSTRACT

In a method for controlling a volume flow of a wetting fluid during adiabatic cooling, an evaporation surface is wetted with the wetting fluid which flows therealong and air to be cooled and/or wetted is directed substantially transversely relative to the flow direction ( 15 ) of the wetting fluid the volume flow of the wetting fluid flowing over the evaporation surface is reduced after a predetermined period of wetting of the evaporation surface and, after the volume flow is reduced, temperatures (T 1 , T 2 ) and/or time/temperature gradients (ΔT 1 , ΔT 2 ) of the directed air are established at least at two different positions in the flow direction substantially parallel with the evaporation surface, with the volume flow of the wetting fluid being controlled in accordance with the established temperatures (T 1 , T 2 ) and/or time/temperature gradients (ΔT 1 , ΔT 2 ).

The invention relates to a method for controlling a volume flow of a wetting fluid during adiabatic cooling, an evaporation surface being wetted with the wetting fluid which flows along the evaporation surface and the air to be cooled and/or to be wetted being directed substantially transversely relative to the flow direction of the wetting fluid over the evaporation surface.

The invention also relates to a device for controlling a volume flow of a wetting fluid during adiabatic cooling, which device has an evaporation surface which can be wetted with the wetting fluid provided by a wetting device and which can exchange heat during the adiabatic cooling and/or wetting with the air to be cooled and/or to be wetted, the volume flow of the wetting fluid which flows along the evaporation surface during cooling and/or wetting being controllable and the air to be cooled and/or to be wetted flowing substantially transversely relative to the flow direction of the wetting fluid and over the evaporation surface.

The invention is in the field of so-called adiabatic cooling which is also called evaporation cooling. During adiabatic cooling, wetting fluid such as, for example, water, is evaporated in order to increase the cooling action. The cooling process uses the physical principle of the energy adsorption of a medium when it changes from the liquid state into the gaseous aggregation state. According to this principle, heat is required for the evaporation of wetting fluid so that it can be cooled by wetting air. A device of the type set out in the introduction is known from the prior art, for example, as a contact wetter or trickling wetter. The method described in the introduction is also known for such a contact wetter, wherein wetting fluid in the form of water is trickled on a porous surface, past which the air to be cooled and/or to be wetted flows, cools and/or absorbs moisture.

Two variants have become established in technical application, so-called direct and indirect adiabatic cooling, also referred to as evaporation cooling. In the case of direct evaporation cooling, the cooling process is implemented by direct wetting of the external air and therefore also of the intake air which is supplied by, for example, a ventilation system. In comparison, the indirect variant brings about the wetting at the discharged air side. The coldness produced is transmitted from the discharged air to the intake air by means of a heat exchanger. This concept has the decisive advantage that the air humidity of the intake air is not changed, that is to say, the relative air humidity does not increase as in the direct method.

During direct and indirect adiabatic cooling, air is wetted adiabatically, that is to say, in a thermally insulated manner or without the supply or discharge of thermal energy. The water required for this, also referred to as wetting fluid, is taken into consideration when the efficiency of the cooling system is considered. With regard to a high level of efficiency of the cooling system, it is necessary to keep the evaporation water consumption or the pump power necessary to convey and circulate the water at a low level. The known systems for cooling air such as, for example, contact wetters or airwashers, have the disadvantage that the water supplied to the process can only be controlled poorly or not at all, but instead the water intake can only be activated for a fixed volume flow by means of a valve control unit or completely deactivated.

Therefore, it is desirable to keep the evaporation water consumption or the pump power of the circulating water flow at a low within an adiabatic cooling and wetting process in order to obtain a high level of efficiency of the cooling and wetting system, an adiabatic cooling process according to the invention being intended to be understood to be a cooling method in which water or wetting fluid is evaporated.

An object of the invention is to increase the efficiency of the control of a volume flow of a wetting fluid during adiabatic cooling with simple means. In particular, an object of the present invention is to provide a method and a corresponding device for controlling a volume flow of a wetting fluid during adiabatic cooling, by means of which substantial improvements can be achieved with suitable means.

In a method of the type set out in the introduction, this object is achieved according to the invention in that the volume flow of the wetting fluid flowing over the evaporation surface is reduced after a predetermined period of wetting of the evaporation surface and, after the volume flow is reduced, temperatures and/or time/temperature gradients of the air directed past the evaporation surface are established at least at two different positions in the flow direction of the wetting fluid substantially parallel with the evaporation surface, with the volume flow of the wetting fluid being controlled in accordance with the established temperatures and/or time/temperature gradients.

The above object is also achieved by a device of the type set out in the introduction in that, in order to control the volume flow of the wetting fluid, there are provided at least two temperature sensors which are arranged downstream of the evaporation surface in the flow direction of the wetting fluid and in relation to the flow direction of the air to be cooled.

The corresponding subsidiary claims relate to advantageous and favorable embodiments and developments of the invention.

The invention provides for a device for controlling a volume flow of a wetting fluid during adiabatic cooling, which device is distinguished by a functionally suitable and simple construction and which further allows control of the actually required volume flow of the wetting fluid. According to the method according to the invention, for controlling a volume flow of a wetting fluid during adiabatic cooling, the control or regulation of the volume flow of the wetting fluid is carried out in accordance with established temperatures which are established and compared at a specific measurement time or in accordance with established time/temperature gradients which are established and determined for a predetermined time period. Temperatures or temperature gradients of the air to be cooled or the air which has already participated in the heat exchange or which has already been cooled and/or wetted are measured or determined downstream of the evaporation surface at least at two positions in the flow direction of the wetting fluid and in relation to the flow direction of the air to be cooled so that there is a type of temperature profile of the cooled and/or wetted air, which indicates whether the evaporation surface is sufficiently wetted with wetting fluid, whereby the desired cooling or wetting is ensured, or whether the evaporation surface has become dry owing to the evaporation of the wetting fluid. In other words, it is possible to establish on the basis of the established temperatures or temperature gradients and the resultant profile in the flow direction of the wetting fluid whether the evaporation of the wetting fluid is carried out to a sufficient extent and uniformly or whether the evaporation surface is wetted with wetting fluid in a non-uniform manner and is even partially already dried out. Therefore, indirect detection of drying out or evaporation in technical measurement terms is possible by virtue of the invention, whereby the control variable is obtained with regard to the supply of wetting fluid. If, for example, the supply of wetting fluid is switched off or the volume flow of the wetting fluid supplied is reduced, a temperature increase must be recorded as a result of drying out at the temperature sensor which is arranged nearest the intake of the wetting fluid.

In an embodiment of the method, the invention provides for a comparison, in order to control the volume flow of the wetting fluid supplied to the evaporation surface, of at least two temperatures which are established at different positions for one measurement time or at least two time/temperature gradients of the air which is intended to be cooled or which has already been cooled and/or which is wetted and has been directed past the evaporation surface, which time/temperature gradients are established at different positions. On the basis of the comparison of the established temperatures or time/temperature gradients which are determined in the flow direction of the wetting fluid, it is readily possible to establish whether evaporation is present or whether the evaporation surface is sufficiently wetted with wetting fluid.

In this regard, the method according to the invention provides in another embodiment for the volume flow of the wetting fluid supplied to the evaporation surface to be controlled in the event of a deviation of at least two temperatures established at different positions for one measurement time or at least two time/temperature gradients established at different positions in respect of the cooled and/or wetted air directed past the evaporation surface. A change of the temperature or the time/temperature gradient of the air directed past the evaporation surface, that is to say, the already cooled and/or wetted air, in the flow direction of the wetting fluid accordingly indicates that the volume flow of the wetting fluid must be controlled and changed.

According to the method according to the invention, the volume flow of the wetting fluid supplied to the evaporation surface is reduced when the established temperatures or the established time/temperature gradients of the air to be cooled and/or to be wetted and directed past the evaporation surface are substantially identical at the at least two different positions in the flow direction of the wetting fluid and substantially transversely relative to the flow direction of the air to be cooled and/or to be wetted, or if the temperatures or time/temperature gradients established at least at two different positions in respect of the air directed past the evaporation surface indicate a temperature increase in the flow direction of the wetting fluid. The temperature increase in the flow direction of the wetting fluid indicates that sufficient wetting fluid is contained in the adiabatic process and that it is possible to dispense with further supply of wetting fluid or the volume flow of the wetting fluid supplied can be reduced accordingly, which may also mean that no wetting fluid at all is supplied.

Conversely, the volume flow of the wetting fluid supplied to the evaporation surface is increased if the temperatures or time/temperature gradients established at the at least two different positions in respect of the air to be cooled and directed past the evaporation surface indicate a temperature increase counter to the flow direction of the wetting fluid. That temperature characteristic in the flow direction of the wetting fluid indicates that the wetted evaporation surface is becoming dried out and accordingly wetting fluid should be supplied to the evaporation surface or the volume flow of the wetting fluid supplied to the evaporation surface should be increased.

In order to avoid a creeping temperature increase during a comparison of the established temperatures or temperature gradients, the invention provides in another embodiment of the method according to the invention for the wetting fluid to be supplied for a predetermined period of time to the evaporation surface at a maximum volume flow or at a volume flow which is increased in comparison with the controlled volume flow. This step is also suitable for reducing occurrences of drying up of minerals and other substances contained in the wetting fluid, calcification and the risk of microbial contamination at the evaporation surface when the adiabatic cooling process and/or the wetting process is/are switched off.

In an embodiment of the method according to the invention, there is further provision for the air to be cooled to be wetted by the wetting fluid and to be cooled in a direct adiabatic manner. The direct wetting of the air to be cooled results in an increase in the air humidity. The control of the volume flow of the wetting fluid is used in conjunction with the direct adiabatic cooling if a high level of humidity is desired for reasons relating to the process such as, for example, in the textile industry or in many painting installations.

Direct adiabatic cooling of the air is possible in a structurally simple manner in that the evaporation surface is a surface of a contact wetter, past which the air to be cooled is directed, which surface can be wetted with wetting fluid.

Alternatively, the evaporation surface may be constructed as a pipe register of an air/fluid heat exchanger in which a heat transfer medium or a heat transfer fluid is directed through the pipe register for adiabatic cooling and/or wetting and the air to be wetted is directed around the pipe register, the outer surface of the pipe register being wetted with wetting fluid during cooling. The wetting brings about so-called excess wetting in the register, by means of which energy for cooling is again released.

In an alternative embodiment, the invention provides for the method for the air which is intended to be cooled to be cooled in an indirect adiabatic manner without exchange of substances with the wetting fluid. To that end, for example, the evaporation surface may be in the form of part of an air/air plate heat exchanger in which cooling air is wetted with the wetting fluid before it is introduced into the air/air plate heat exchanger. The cooling air can be wetted, for example, by means of a contact wetter according to the principle of direct adiabatic cooling so that it is readily possible to combine very efficiently different concepts of cooling, that is to say, adiabatic direct and indirect cooling.

In order to control an excess quantity of wetting fluid always present during wetting, it is provided in an embodiment of the method for the temperatures to be established by means of corresponding temperature sensors, the temperature sensors for the comparison of established temperatures before the evaporation surface is wetted and before the adiabatic cooling being calibrated in such a manner that the temperature sensors have, before the wetting begins, a desired temperature difference in the flow direction of the wetting fluid. That preset temperature difference is selected in such a manner that, before the wetting and before the adiabatic cooling, an apparent temperature increase counter to the flow direction is indicated, which signifies an increase of the volume flow of the wetting fluid supplied.

With regard to the device according to the invention, in an embodiment the evaporation surface may be a surface of a contact wetter, which surface can be wetted with the wetting fluid, and the cooling of the air to be cooled can be carried out in a direct adiabatic manner.

According to another embodiment of the device according to the invention, the evaporation surface is in the form of a pipe register of an air/fluid heat exchanger, in which a heat transfer medium or a heat transfer fluid flows through the pipe register and the air to be cooled flows around the pipe register, the air/fluid heat exchanger having the wetting device by means of which the external surface of the pipe register can be wetted with the wetting fluid. The wetting device may be in the form of a washer, contact wetter, high-pressure wetter or the like.

According to still another embodiment of the device according to the invention, the evaporation surface is in the form of part of an air/air plate heat exchanger, in which the air to be cooled exchanges its heat in an indirect adiabatic manner with cooling air which is wetted with the wetting fluid before it is introduced into the air/air plate heat exchanger. In this instance, the cooling air can be wetted, for example, by means of a contact wetter.

Finally, the invention provides in another embodiment of the device for the at least two temperature sensors to be arranged outside the air/air plate heat exchanger at the outlet side for the air to be cooled. An indirect temperature measurement of the drying out action thereby follows because the air so be cooled is not wetted in this procedure.

It will be understood that the features mentioned above and those which will be explained below can be used not only in the combination set out but also in other combinations or alone without departing from the scope of the present invention. The scope of the invention is defined only by the claims.

Additional details, features and advantages of the subject-matter of the invention will be appreciated from the following description with reference to the drawings, in which preferred embodiments of the invention are illustrated by way of example and in which:

FIG. 1 is a schematic illustration of a device according to the invention which is in the form of a contact wetter,

FIG. 2 is an exemplary illustration of an application in which the established temperatures or temperature gradients of the air to be cooled increase in the flow direction of the wetting fluid,

FIG. 3 is an exemplary illustration of another application in which the established temperatures or temperature gradients of the air to be cooled increase counter to the flow direction of the wetting fluid,

FIG. 4 is a schematic illustration of another device according to the invention which is in the form of an air/fluid heat exchanger and

FIG. 5 is a schematic illustration of still another device according to the invention which is in the form of an air/air heat exchanger.

FIGS. 1, 4 and 5 illustrate different devices according to the invention for the adiabatic cooling of air, the device in FIG. 1 being in the form of a contact wetter 10, the device in FIG. 4 being in the form of an air/fluid heat exchanger 20 and the device in FIG. 5 being in the form of an air/air heat exchanger 30.

The device according to the invention in the form of a contact wetter 10 in FIG. 1 has an evaporation surface 11 which is in the form of a porous surface 12. The surface 12 of the evaporation surface 11 can be wetted with wetting fluid, the evaporation surface 11 being connected to a wetting device 13. Wetting fluid is supplied to the wetting device 13 via an intake 14. Furthermore, the wetting device 13 provides wetting fluid for the evaporation surface 11 so that it can be wetted. The arrow 15 in FIG. 1 indicates the flow direction of the wetting fluid which is produced as a result of the influence of gravitational force, the evaporation surface 11 being intended for wetting and for heat exchange with air to be wetted and cooled. The flow direction of the air to be cooled and wetted is indicated by arrows 16 a and 16 b in FIG. 1. The arrow 16 a relates to the air which is still intended to be cooled and which is upstream of the evaporation surface 11 in relation to the flow direction of the air to be cooled, whereas the arrow 16 b relates to the already cooled air which is downstream of the evaporation surface 11 in relation to the flow direction of the air to be cooled and wetted. Therefore, the arrow 16 b indicates the flow direction of the cooled and/or wetted air which has already passed the evaporation surface 11. Consequently, the air to be cooled and/or wetted is directed past the surface 12 of the contact wetter 10, which surface can be wetted with wetting fluid, or flows past it at that location. Accordingly, the wetting fluid and the air to be cooled are substantially directed with cross-flow, the evaporation surface 11 exchanging heat with the air to be cooled during adiabatic cooling so that there is direct adiabatic cooling of the air to be cooled for this embodiment, whereby the air humidity of the air to be cooled increases during cooling. Consequently, the wetting fluid flows along the evaporation surface during adiabatic cooling, with the air to be cooled flowing over the evaporation surface 11 substantially transversely relative to the flow direction (arrow 15 in FIG. 1) of the wetting fluid. Excess wetting fluid or wetting fluid which does not evaporate during the heat exchange with the air to be cooled is collected by a collector 17 under the evaporation surface 11 as a result of the influence of gravitational force and is directed back in a circuit to the intake 14 of the wetting device 13 via an outlet 18 by means of a pump (not illustrated) in order to further supply the evaporation surface 11 with wetting fluid and to wet it. The volume flow of the wetting fluid which is supplied to the evaporation surface 11 via the wetting device 13 can be controlled by the supply of wetting fluid being switched on or switched off. However, a wetting fluid supply which is adapted to requirements and optionally continuous is currently unknown, the requirement being intended to be orientated towards the degree of evaporation of the evaporation fluid.

In order to reduce the consumption of the wetting fluid and/or the necessary pump power for circulating or recycling the wetting fluid, the invention makes provision for at least two temperature sensors 19 a and 19 b to be provided in order to control the volume flow of the wetting fluid. FIG. 1 schematically indicates a third temperature sensor 19 c which may be omitted and merely serves to increase the sensitivity of detection of the drying out or evaporation. The temperature sensors 19 a, 19 b and optionally 19 c are arranged downstream of the evaporation surface 11 in the air flow of the cooled and/or wetted air in the flow direction of the wetting fluid (arrow 15 in FIG. 1) and in relation to the flow direction of the air to be cooled (arrow 16 b in FIG. 1).

In order to reduce the consumption of the wetting fluid and the pump power, the method according to the invention is described below with reference to FIG. 1, in which an adiabatic process is schematically illustrated with reference to the contact wetter 10. As already set out above, the evaporation surface 11 is wetted with wetting fluid. The air to be cooled and/or to be wetted flows substantially transversely (see arrow 16 a in FIG. 1) relative to the flow direction 15 of the wetting fluid in the direction of and over the evaporation surface 11. After a predetermined wetting time, during which the surface 12 of the evaporation surface 11 is adequately wetted with wetting fluid in accordance with experience with regard to the adiabatic cooling, the volume flow of the wetting fluid supplied to the evaporation surface 11 via the wetting device 13 is reduced, it being possible for the reduction also to include the supply of wetting fluid being switched off. When the volume flow of the wetting fluid is reduced, the evaporation surface of the contact wetter slowly begins to dry out if insufficient wetting fluid is supplied or if the reduction of the supplied wetting fluid is excessive. The cooling action of the process decreases continuously with the drying action, which results in a higher temperature of the air to be cooled downstream (see arrow 16 b in FIG. 1) of the evaporation surface 11. In other words, due air to be cooled and/or to be wetted is no longer sufficiently cooled and has an excessively high temperature after passing the evaporation surface 11.

The drying out at the evaporation surface 11 begins in the region of the wetting device 13 and continues in the flow direction 15 of the wetting fluid. It is possible to detect the beginning of a drying out action in technical measurement terms by means of at least two temperature sensors 19 a and 19 b. It is further possible to use additional temperature sensors arranged in the flow direction of the wetting fluid such as, for example, the third temperature sensor 19 c, in order to be able to detect the drying out more precisely. In the embodiment illustrated in FIG. 1, the temperature sensors 19 a, 19 b, 19 c, are arranged in the flow direction 15 of the wetting fluid parallel with the evaporation surface 11 and downstream of the evaporation surface 11 in relation to the flow direction of the air to be cooled (see arrow 16 b in FIG. 1). In more abstract terms, after the reduction of the volume flow of the wetting fluid, temperatures of the air which is intended to be cooled and which is directed past the evaporation surface 11 are established by means of at least two temperature sensors 19 a, 19 b (optionally also 19 c) at least at two different positions in the flow direction 15 of the wetting fluid parallel with the evaporation surface 11. The volume flow of the wetting fluid supplied via the wetting device then controlled in accordance with the temperatures established for a measurement time. For that purpose, the temperatures of the air which has passed the heat exchanger 11, which temperatures are measured by the at least two temperature sensors 19 a, 19 b (optionally also 19 c) for one measurement time, are compared with each other. Owing to the evaporation surface 11 drying out, which first takes place in the region of the wetting device 13 and then continues in the flow direction 15 of the wetting fluid, the temperature of the temperature sensor 19 a will be higher and/or will increase more powerfully than for the temperature sensors 19 b and 19 c. If such a temperature increase is detected, the volume flow of the wetting fluid supplied must be increased in order to act counter to the evaporation. After the volume flow has been increased, the temperature of the first temperature sensor 19 a then decreases, if the supply of wetting fluid is sufficient, to the level of the subsequent temperature sensor 19 b or 19 c which is arranged in the flow direction 15 of the wetting fluid and it is thereby indicated that the surface 12 of the evaporation surface 11 is sufficiently wetted with wetting fluid and that the volume flow of the wetting fluid supplied to the evaporation surface 11 can be reduced again.

In other words, the volume flow of the wetting fluid is controlled on the basis of the comparison of the temperatures measured downstream of the evaporation surface 11 in respect of the air to be cooled or cooled air, wherein control is only brought about if the at least two temperatures established for a measurement time at different positions (that is to say, at the positions of the temperature sensors 19 a and 19 b or 19 c) in respect of the air which is intended to be cooled and which is directed past the evaporation surface 11 differ from each other.

The volume flow of the wetting fluid supplied to the evaporation surface 11 is reduced if the established temperatures of the air to be cooled and the air directed past the evaporation surface 11 are substantially identical at the at least two different positions in the flow direction 15 of the wetting fluid and substantially transversely relative to the flow direction of the air to be cooled or if the temperatures established at least at two different positions in respect of the air to be cooled and the air to be directed past the evaporation surface 11 indicate a temperature increase in the flow direction 15 of the wetting fluid because those conditions indicate that enough wetting fluid is present in the process. This case is illustrated by way of example in the graph of FIG. 2, where the temperatures or temperature gradients of the air to be cooled are indicated downstream of the heat exchange surface 11 (arrow 16 b) in the flow direction FR_(BF) or 15 of the wetting fluid. As can be seen, the temperature increases from the value T₁ at the position of the first temperature sensor 19 a as far as the position of the second temperature sensor 19 b to T₂.

The volume flow of the wetting fluid supplied to the evaporation surface 11 further increased if the temperatures established at the at least two different positions in respect of the air to be cooled and the air directed past the evaporation surface 11 indicate a temperature increase counter to the flow direction 15 of the wetting fluid, as already set out above for the scenario of drying out. This case is illustrated by way of example in the graph of FIG. 3. As can seen in the graph, the temperature T₁ established by the first temperature sensor 19 a decreases in the flow direction FR_(BF) or 15 of the wetting fluid as far as the second temperature sensor 19 b to the temperature T₂ and it is thereby indicated that the evaporation surface 11 is not wetted enough but is instead dried out. The volume flow of the wetting fluid supplied to the evaporation surface 11 is increased as a corresponding step in order to act counter to the drying out.

The graphs of FIGS. 2 and 3 show that, in order to control the volume flow of the wetting fluid supplied to the evaporation surface 11, the temperature profile of the air which has passed the evaporation surface 11 (air flow which is indicated by the arrow 16 b in FIG. 1) is determined, wherein for that purpose temperatures are established at least at two positions downstream of the evaporation surface 11 in the flow direction 15 of the wetting fluid and in relation to the flow direction of the air to be cooled, and the temperatures directly produce the temperature profile. Alternatively, it is also possible to determine from the established temperatures which are measured at a predetermined time interval Δt time/temperature gradients ΔT, that is to say, ΔT (Δt), from which the temperature profile illustrated in FIGS. 2 and 3 is then derived.

Consequently, time/temperature gradients ΔT(Δt) can alternatively also be determined by means of the temperature sensors 19 a, 19 b, 19 c in order to control the volume flow of the supplied wetting fluid. The temperature gradients ΔT (Δt) reflect a comparison of the temperature change over time of the air to be cooled downstream of the evaporation surface 11. The volume flow of the wetting fluid is controlled in the case of the comparison of the time/temperature gradients ΔT (Δt) similarly to the above manner in the case of the comparison of the established temperatures T₁ and T₂, wherein FIGS. 2 and 3 and the description thereof are also valid when temperature gradients ΔT₁ and ΔT₂ are used so that reference may be made to the above description with regard to the control. The advantage during analysis and evaluation of the time/temperature gradients ΔT (Δt) is that drying out can be detected more rapidly and calibration of the temperature sensors 19 a, 19 b, 19 c with respect to each other is not necessary.

By the temperatures being continuously measured by means of the temperature sensors 19 a, 19 b, 19 c in the flow direction 15 downstream of the evaporation surface 11 and the comparison of the temperatures and/or time/temperature gradients, which comparison is carried out on the basis of those data, the above-described method for controlling the volume flow of the wetting fluid can then be carried out over the entire duration of the adiabatic cooling process, the process illustrated in FIG. 1 for the contact wetter 10 being a direct adiabatic cooling operation.

FIG. 4 illustrates by way of example an adiabatic cooling process by means of an air/fluid heat exchanger 20 which has the evaporation surface 11, an intake 21 for supplying the evaporation surface 11 in the form of a pipe register 22 (in FIG. 4, the register 22 is merely indicated by way of example) with a heat transfer medium and an outlet 23 for the heat transfer medium directed through the pipe register 22. The air of the adiabatic cooling process flows laterally into and through the air/fluid heat exchanger 20 and flows around the pipe register 22 before the air is then laterally discharged again out of the air/fluid heat exchanger 20. In the air/fluid heat exchanger 20, there is further provided the wetting device 13 by means of which the outer surface of the pipe register 22 is wetted with the wetting fluid during adiabatic cooling in order to achieve excessive wetting in the pipe register 22 or in the air/fluid heat exchanger 20, whereby energy for cooling is again released. As a result of gravitational force, excess wetting fluid reaches the collector 17 under the evaporation surface 11 before it is directed back in a circuit to the intake 14 of the wetting device 13 via the outlet 18 by means of a pump which is not illustrated. The air which is used and wetted also flows again in accordance with the arrows 16 a and 16 b and substantially transversely relative to the flow direction 15 of the wetting fluid through the air/fluid heat exchanger 20, the air to be wetted being directed around the pipe register during adiabatic cooling. The method carried out with the air/fluid heat exchanger 20 for controlling the volume flow of the supplied wetting fluid is also based on a measurement of temperatures of the wetted air downstream of the evaporation surface 11 by means of the at least two temperature sensors 19 a and 19 b (and optionally the additional third temperature sensor 19 c) and similarly corresponds to the above-described control method for the contact wetter 10 so that repetition of the explanations is omitted and instead reference is made to the above description. The embodiment illustrated in FIG. 4 of the air/fluid heat exchanger 20 with a pipe register 22 through which a heat transfer medium flows can be used to wet the air which flows round the pipe register 22 and also to cool it so that the heat transfer medium absorbs the heat of the air. Alternatively, it is conceivable to have an application in which, although the air which flows through the air/fluid heat exchanger 20 is also wetted, the air absorbs heat from the heat transfer medium which flows through the pipe register 22 so that cooling of the heat transfer medium is brought about and the temperature of the wetted air increases. The heated air would then be discharged to the environment in such a procedure.

Another embodiment of a device according to the invention is shown in FIG. 5 which is in the form of an air/air plate heat exchanger 30 in this instance. In this instance, the evaporation surface 11 is in the form of part of the air/air plate heat exchanger 30, the cooling of the air being carried out in an indirect adiabatic manner in contrast to the two preceding embodiments and wetting of the air to be cooled stopping. The air/air plate heat exchanger 30 has the wetting device 13 which wets a cooling air flow 31 with the wetting fluid before it is introduced into the air/air plate heat exchanger 30. The cooling air flow 32 which is discharged from the air/air plate heat exchanger 30 is then discharged into the open air, for example, and does not participate any further in the cooling process. The situation with the wetting fluid which wets the cooling air flow 31 which is introduced into the air/air plate heat exchanger 30 is different. The excess wetting fluid flows through the air/air plate heat exchanger 30 as a result of gravitational force and, at the discharge side, reaches the collector 17 below the air/air plate heat exchanger 30. The wetting fluid can then either be discharged from the system or the device via the outlet 18 or be conveyed by means of a pump back to the wetting device 13, as already described above for the other embodiments. The air to be cooled is again directed substantially transversely relative to the flow direction 15 of the wetting fluid (see arrows 16 a and 16 b in FIG. 3). In order to determine the extent of drying out, the temperatures of the cooled air (the air flow indicated with the arrow 16 b in FIG. 3) are measured downstream of the air/air plate heat exchanger 30 by means of the temperature sensors 19 a, 19 b and optionally 19 c. Consequently, the temperature sensors 19 a, 19 b and optionally 19 c are arranged outside the air/air plate heat exchanger 30 at the outlet side 33 thereof for the air to be cooled or in order to measure the temperature of the air which has been cooled, the air to be cooled not absorbing any moisture in comparison with the above two embodiments because a direct exchange between the air to be cooled and the wetting fluid does not take place.

In the case of the air/air plate heat exchanger 30, the heat exchange takes place between the air to be cooled and the cooling air flow 31 which is wetted with wetting fluid before it is introduced into the air/air plate heat exchanger 30 in an adiabatic indirect manner. The excess wetting fluid which is not absorbed by the cooling air flow 31 flows in the vertical flow direction 15 through the air/air plate heat exchanger 30 and is collected at the outlet side by the collector 17. The volume flow of the wetting fluid is controlled by the wetting device 13 in the same manner as already described for the other two embodiments so that a detailed description of the method is omitted in order to avoid repetition. Instead, reference is made to the explanations relating to the first embodiment of the contact wetter 10, where the individual method steps for controlling the volume flow of the wetting fluid were described in great detail.

It should be noted that the term “device” (contact wetter 10, air/fluid heat exchanger 20 and air/air plate heat exchanger 30) is intended according to the invention to be understood to be a system comprising at least an evaporation surface 11, wetting device 13 and collector 17, which cooperate for the purpose of the adiabatic cooling of air.

In conclusion, an adiabatic process has been described above for a first embodiment in the form of a contact wetter 10 which comprises a wetted structure in its interior. In order to improve the evaporation of the water or the wetting fluid, an air flow of air to be cooled is directed over the structure or surface 12 of the contact wetter 10. The water or the wetting fluid which is used for wetting is brought into the structure via the intake 14 and the wetting device 13 and flows away on it as a result of gravitational force. In order to prevent calcification of the structure or surface 12, wetting is carried out with an excess of water. The excess water or the excess wetting fluid runs off from the contact wetter 10 and leaves the process. The wetted element or the wetted surface 12 which constitutes an evaporation surface 11 takes up water or wetting fluid by virtue of its great surface 12 and the surface tension of the water and/or by virtue of the porous structure thereof and stores it.

If the water supply or the supply of wetting fluid to the element to be wetted which constitutes the evaporation surface 11 is switched off or the supplied volume flow of the wetting fluid is reduced, the element begins to slowly dry out owing to the stored wetting fluid and the cooling action of the device continuously decreases. That reduction in cooling action results in higher temperatures in accordance with the adiabatic process. The drying out action begins in the flow direction 15 of the wetting fluid, starts in the region of the wetting device 13 (the water supply) and continues in the flow direction 15 of the wetting fluid in the element. It is possible to detect the drying out in technical measurement terms by a plurality of temperature sensors 19 a, 19 b, 19 c with at least two temperature sensors being necessary and being arranged downstream of the evaporation surface 11 in the flow direction 15 of the wetting fluid in relation to the flow direction of the air to be cooled. A distinction is made between at least the upper temperature sensor (19 a) and the lower temperature sensor (19 b). Additional temperature sensors 19 c may further be used in the flow direction 15 of the wetting fluid in order to be able to detect the drying out more precisely.

By means of that indirect detection of the drying out in technical measurement terms, the control variables for switching on and switching off the water intake (wetting fluid) or controlling the circulating water flow are provided. If the wetting water supply is switched off or is reduced in terms of volume flow, the temperature initially increases in the element as a result of drying out at the nearest temperature sensor 19 a in relation to the wetting location (that is to say, in the region of the wetting device 13). If that temperature increase in comparison with the temperature sensor 19 b or 19 c which is nearest in the flow direction 15 is detected, the wetted element begins to dry out. If such a temperature increase is detected, the water intake must be opened or the circulating water flow must be increased. After a specific time, the temperature of the first temperature sensor 19 a in relation to the wetting location decreases to the level of the subsequent temperature sensor 19 b or 19 c and the element is again completely wetted. It is again possible to switch off the water supply or the supply of wetting fluid or to reduce the water flow or the volume flow of the wetting fluid, and the control process can be carried out again as described.

In addition to the described temperature comparison between the temperature sensors 19 a, 19 b, 19 c, a comparison of the temperature change-overtime is also possible in order to control the wetting water quantity or the volume flow of the wetting fluid. Those temperature gradients are used in a similar manner to that described. The advantage of the temperature gradients is that detection of drying out is more rapid and calibration of the temperature sensors 19 a, 19 b, 19 c relative to each other is unnecessary. The temperature sensors 19 a, 19 b, 19 c can also be arranged at the non-wetted side of the air to be cooled in the case of an air/air (cross flow) heat exchanger.

A control system for adiabatic cooling of air has been set out above and operates by means of temperature sensors 19 a, 19 b, 19 c which are arranged with the flow direction 15 of the wetting water or the wetting fluid at the air discharge side of the contact wetter 10 or a wetted fluid/air heat exchanger 20 or at the non-wetted air side of the air/air cross flow heat exchanger 30 (indirect measurement). The control system serves to reduce the excessive water volume flow being discharged or to reduce the pump power in a circulating water system. The process is controlled with regard to the wetting water consumption (consumption of the wetting fluid) or the circulating pump power in accordance with the air conditions by the water or the wetting fluid being switched off and on by means of the intake 14 into the adiabatic process or being controlled in terms of water volume flow.

After a temperature comparison of the temperature sensor nearest the water supply (upper temperature sensor 19 a) with a temperature sensor downstream in the flow direction 15 of the wetting water (for example, lower temperature sensor 19 b or middle temperature sensor 19 c), the wetting water is switched on or off by means of the intake 14 or circulating water volume flow is controlled in accordance with the deviation thereof.

If the temperature of the temperature sensor 19 a nearest the water supply 13 to the wetted element (that is to say, the heat exchange surface 11) into the adiabatic process is higher with respect to the subsequent temperature sensors 19 b or 19 c, drying out occurs in the wetted element and water or wetting fluid must be switched on via the intake 14 or the circulating water volume flow must be increased.

If the temperature of the temperature sensor 19 a nearest the water inlet (intake 14) into the adiabatic process is lower or identical with respect to the downstream temperature sensors 19 b or 19 c, enough water/wetting fluid is present in the adiabatic process and the water or the wetting fluid can be switched off via the intake 14 or the flow quantity or the volume flow can be reduced.

By the temperature sensors 19 a, 19 b and optionally 19 c being calibrated, a deliberate temperature difference can be obtained between the temperature sensors 19 a, 19 b, 19 c, whereby the excess water quantity or wetting fluid can be controlled. In other words, in order to control an excess quantity of wetting fluid always present during wetting, the temperature sensors 19 a, 19 b can calibrated for the comparison of the established temperatures T₁, T₂ before the evaporation surface 11 is wetted and before the adiabatic cooling in such a manner that the temperature sensors 19 a, 19 b have a desired temperature difference in the flow direction 15 of the wetting fluid before the beginning of the wetting. That preset and desired temperature difference between the temperature sensors 19 a, 19 b is selected in such a manner that, before the wetting and before the adiabatic cooling, an apparent temperature increase counter to the flow direction 15 is indicated, which signifies an increase of the volume flow of the supplied wetting fluid. If the adiabatic cooling process and the wetting provided therefor are then started, the preset and desired temperature difference ensures that a given excess of wetting fluid is always present and acts counter to drying in of substances contained in the water on the evaporation surface 11.

In accordance with the method, the wetting water or the wetting fluid is switched on or off via the intake 14 or is controlled and reduced in terms of the circulating water volume flow after a temperature gradient comparison of the temperature sensor 19 a (upper temperature sensor) nearest the water supply (intake 14) with a temperature sensor 19 b or 19 c downstream in the flow direction 15 of the wetting water in accordance with the deviation.

If the temperature gradient of the temperature sensor 19 a nearest the water supply to the wetting element (evaporation surface 11) into the adiabatic process is higher with respect to the downstream temperature sensors 19 b or 19 c, drying out occurs in the wetted element (evaporation surface 11) and water/wetting fluid must be switched on via the intake 14 or the circulating water volume flow must be increased.

If the temperature gradient of the temperature sensor 19 a nearest the water inlet (intake 14) in the adiabatic process lower or identical with respect to the subsequent temperature sensors 19 b or 19 c, enough water/wetting fluid is present in the adiabatic process and the water or wetting fluid can be switched off via the intake 14 or can be reduced in terms of volume flow.

In order to prevent a creeping temperature increase from the temperature gradient comparisons, the intake water is switched on for an adjustable time or wetting is carried out with the maximum possible water flow.

In order to further reduce drying in of minerals and other substances contained in the water or the wetting fluid in the wetted element, the wetting water onto the element to be wetted is continued for an adjustable time and subsequently switched off after the adiabatic cooling process has been switched off.

In all the embodiments illustrated and all the conceivable developments thereof, the volume flow of the supplied wetting fluid can be controlled by means of corresponding valves for switching on and off or corresponding control valves for controlling the volume flow, for example, at the wetting device 13, or by means of a speed-controlled pump. Furthermore, the wetting fluid may be supplied to the evaporation surface 11 with a maximum volume flow for a predetermined time in order to prevent drying in of minerals or occurrences of calcification at the evaporation surface 11 after the adiabatic cooling process has finished. However, the supply at maximum volume flow of the wetting fluid, which supply is provided for a predetermined time may also serve to prevent a creeping temperature increase during the temperature gradient comparison.

According to the invention, the expression of “controlling a volume flow of a wetting fluid” which is used in the above description and in the claims in order to designate the method and the device is equivalent to the expressions “controlling the humidity of air” or even “air humidity control”, wherein the control is carried out in each case in the context of an adiabatic cooling process in which the air whose adequate humidity must be ensured is used. The method according to the invention and the device suitable for the method are used to control the wetting of the air used during the adiabatic cooling in accordance with the beginning of drying out of the evaporation surface by means of the volume flow supplied to the evaporation surface.

The above-described invention is naturally not limited to the embodiments described and illustrated. It is apparent that a large number of modifications which are obvious to the person skilled in the art in accordance with the intended use can be carried out with respect to the embodiments illustrated in the drawings without the scope of the invention thereby being exceeded. The invention includes everything which is contained in the description and/or which is illustrated in the drawings including anything obvious to the person skilled in the art in a manner deviating from the specific embodiments. 

1. Method for controlling a volume flow of a wetting fluid during adiabatic cooling, an evaporation surface being wetted with the wetting fluid which flows along the evaporation surface and the air to be cooled and/or to be wetted being directed substantially transversely relative to the flow direction of the wetting fluid over the evaporation surface, wherein the volume flow of the wetting fluid flowing over the evaporation surface is reduced after a predetermined period of wetting of the evaporation surface and, after the volume flow is reduced, temperatures (T₁, T₂) and/or time/temperature gradients (ΔT₁, ΔT₂) of the air directed past the evaporation surface are established at least at two different positions in the flow direction of the wetting fluid substantially parallel with the evaporation surface, with the volume flow of the wetting fluid being controlled in accordance with the established temperatures (T₁, T₂) and/or time/temperature gradients (ΔT₁, ΔT₂).
 2. Method according to claim 1, wherein, in order to control the volume flow of the wetting fluid supplied to the evaporation surface, at least two temperatures (T₁, T₂) which are established at different positions for one measurement time or at least two time/temperature gradients (ΔT₁, ΔT₂) of the air which is directed past the evaporation surface, which time/temperature gradients (ΔT₁, ΔT₂) are established at different positions, are compared.
 3. Method according to claim 1 wherein the volume flow of the wetting fluid supplied to the evaporation surface is controlled in the event of a deviation of at least two temperatures (T₁, T₂) established at different positions for one measurement time or at least two time/temperature gradients (ΔT₁, ΔT₂) established at different positions in respect of the air directed past the evaporation surface.
 4. Method according to claim 1, wherein the volume flow of the wetting fluid supplied to the evaporation surface is reduced when the established temperatures (T₁, T₂) or the established time/temperature gradients (ΔT₁, ΔT₂) of the air directed past the evaporation surface are substantially identical at the at least two different positions in the flow direction of the wetting fluid and substantially transversely relative to the flow direction of the air to be cooled, or if the temperatures (T₁, T₂) or time/temperature gradients (ΔT₁, ΔT₂) established at least at two different positions in respect of the air directed past the evaporation surface indicate a temperature increase in the flow direction of the wetting fluid.
 5. Method according to claim 1, wherein the volume flow of the wetting fluid supplied to the evaporation surface is increased if the temperatures (T₁, T₂) or time/temperature gradients (ΔT₁, ΔT₂) established at the at least two different positions in respect of the air directed past the evaporation surface indicate a temperature increase counter to the flow direction of the wetting fluid.
 6. Method according to claim 1, wherein the wetting fluid is supplied for a predetermined period of time to the evaporation surface at a volume flow which is increased in comparison with the controlled volume flow.
 7. Method according to claim 1, wherein the evaporation surface is a surface of a contact wetter, past which the air to be cooled is directed, which surface can be wetted with wetting fluid.
 8. Method according to claim 1, wherein the evaporation surface is constructed as a pipe register of an air/fluid heat exchanger in which a heat transfer medium is directed through the pipe register for adiabatic cooling and the air to be wetted is directed around the pipe register, the outer surface of the pipe register being wetted with wetting fluid during cooling.
 9. Method according to claim 1, wherein the evaporation surface is in the form of part of an air/air plate heat exchanger in which cooling air is wetted with the wetting fluid before it is introduced into the air/air plate heat exchanger.
 10. Method according to claim 1, wherein the temperatures (T₁, T₂) are established by means of corresponding temperature sensors, the temperature sensors for the comparison of established temperatures (T₁, T₂) before the evaporation surface is wetted and before the adiabatic cooling being calibrated in such a manner that the temperature sensors have, before the wetting begins, a desired temperature difference in the flow direction of the wetting fluid.
 11. Device for controlling a volume flow of a wetting fluid during adiabatic cooling, which device has an evaporation surface which can be wetted with the wetting fluid provided by a wetting device and which can exchange heat during the adiabatic cooling and/or wetting with the air to be cooled and/or to be wetted, the volume flow of the wetting fluid which flows along the evaporation surface during cooling and/or wetting being controllable and the air to be cooled and/or to be wetted flowing substantially transversely relative to the flow direction of the wetting fluid and over the evaporation surface, wherein, in order to control the volume flow of the wetting fluid, there are provided at least two temperature sensors which are arranged downstream of the evaporation surface in the flow direction of the wetting fluid and in relation to the flow direction of the air to be cooled.
 12. Device according to claim 11, characterized in that the evaporation surface is a surface of a contact wetter, which surface can be wetted with the wetting fluid, and in that the cooling of the air to be cooled is carried out in a direct adiabatic manner.
 13. Device according to claim 11, wherein the evaporation surface is in the form of a pipe register of an air/fluid heat exchanger, in which a heat transfer medium flows through the pipe register and the air to be cooled flows around the pipe register, the air/fluid heat exchanger having the wetting device by means of which the external surface of the pipe register can be wetted with the wetting fluid.
 14. Device according to claim 11, wherein the evaporation surface is in the form of part of an air/air plate heat exchanger, in which the air to be cooled exchanges its heat in an indirect adiabatic manner with cooling air which is wetted with the wetting fluid before it is introduced into the air/air plate heat exchanger.
 15. Device according to claim 11, wherein the at least two temperature sensors are arranged outside the air/air plate heat exchanger at the outlet side for the air to be cooled. 